When a fountain pen is onboard an aircraft, it can leak ink due to the strong pressure difference inside the pen vs. outside the pen. This can result in messes to clean up on the flight even if the pen is not used, and at best ink blots when it is used.
Most of the advice I've been seeing about bringing fountain pens onto airplanes is that one should either completely fill them, or leave them completely empty before boarding the plane. However, this only works for storing the pen while in flight, and not for actually using the pen while in flight.
How can I effectively use a fountain pen while on an airplane? Is the only way to leave it empty and to fill it while onboard? I can think of a design for a pen that would allow it to be used on a plane effectively (store the ink in a bladder that changes size), but are there any pens that work like that?